Most snowmobiles include a chassis, an engine, a transmission, and endless belt assembly designed to contact the ground and propel the snowmobile. Typical snowmobiles also include a pair of front skis support by a front suspension system. The endless belt assembly generally includes a rear suspension system designed to help the belt assembly maintain contact with the ground when riding over uneven terrain and provide the rider with a comfortable ride.
Generally, there are two types of snowmobile rear suspensions in the snowmobile industry: coupled and uncoupled. The term “coupled” is generally given to suspensions that have dependant kinematics front-to-rear and/or rear-to-front relative to the lower rails of the rear suspension. A suspension is coupled rear-to-front when the front portion of the lower rails is deflected vertically and the rear portion of the lower rails is forced to move vertically to some degree. A suspension is coupled rear-to-front when the rear portion of the lower rails is deflected vertically and the front portion of the lower rails is forced to move vertically to some degree. An uncoupled rear suspension is generally independent front-to-rear and rear-to-front relative to the lower rails of the rear suspension. A vertical deflection of the front portion of the suspension causes little to no vertical deflection of the rear portion of the suspension and vice versa.
Coupled suspensions differ from uncoupled suspension in at least two areas. There is a distinct stiffness or rate of deflection of the rear suspension per pound of force applied to the rear suspension for both the front and rear portion of the rear suspension. A coupled suspension combines the rates of both the front and rear portions of the rear suspension so the overall rate becomes higher than rate that may be achieved with an uncoupled rear suspension. Second, a coupled rear suspension may be used to control weight transfer to the rear suspension during acceleration of the snowmobile.